1. Field of the Invention
The present invention relates to a white organic electroluminescent (EL) device having a green sub-emission layer, a red sub-emission layer, and a blue sub-emission layer, the layers being laminated.
2. Description of the Related Art
White organic EL devices having the following characteristics have been developed: the devices each have a green sub-emission layer, a red sub-emission layer, and a blue sub-emission layer, the layers being laminated, and lights emitted from the respective layers undergo color mixture so that white light may be emitted.
Japanese Patent Application Laid-Open No. H06-207170 describes a white organic EL device in which light emission from each of sub-emission layers is caused by a fluorescent light emitting material in the sub-emission layer.
In addition, Japanese Patent Application Laid-Open No. 2004-241374 describes an organic EL device having a delayed fluorescent material.
A reduction in driving voltage of a white organic EL device having the following characteristics has been required: the device has a green sub-emission layer, a red sub-emission layer, and a blue sub-emission layer, the layers being laminated, and lights emitted from the respective layers undergo color mixture so that white light may be emitted.
Japanese Patent Application Laid-Open No. 2004-241374 describes the organic EL device having the delayed fluorescent material, but does not describe a white organic EL device having the following characteristics: the device has a green sub-emission layer, a red sub-emission layer, and a blue sub-emission layer, the layers being laminated, and lights emitted from the respective layers undergo color mixture so that white light may be emitted. In addition, the delayed fluorescent material in Japanese Patent Application Laid-Open No. 2004-241374 shows each of a strong delayed fluorescent spectrum and a strong phosphorescent spectrum in the range of 520 nm to 750 nm, and an emission wavelength actually illustrated in the figure is formed of a peak having a maximum emission wavelength in excess of 550 nm and a peak having a maximum emission wavelength in excess of 600 nm. That is, the delayed fluorescent material is not a light emitting material that emits light of a primary color such as a green or blue color in view of its color purity.